In gastroenterology, irritable bowel synrome (IBS) is a functional bowel disorder characterized by abdominal pain, discomfort or bloating relieved by defecation and alteration of bowel habits. Diarrhea or constipation may predominate, or they may alternate (classified as IBS-D, IBS-C or IBS-A, respectively). IBS may begin after an infection (post-infectious, IBS-PI) or a stressful life event. Other functional or pain disorders and certain psychological conditions are more common in those with IBS.